Re: [RFC PATCH for 4.17 02/21] rseq: Introduce restartable sequences system call (v12)

On Thu, 29 Mar 2018 14:02:33 -0400 (EDT)
Mathieu Desnoyers [off-list ref] wrote:

Currently, anyone using ptrace on a process has pretty much given up all
hopes of performance. Processes will use rseq to gain performance, not the
opposite, so this deterioration will be unwelcome.

The ptrace path has nothing to do with ptrace anymore, and probably be
hard to notice the performance hit. You simply set a TIF flag, and on
exit of the syscall it jumps to a path that checks special cases
(tracing system calls being one of them). It's called the ptrace path
because ptrace was the first one to use it (I'm guessing, I haven't
actually looked at the history).

This is used to add any system call checks that are not done during
normal operation. And this certainly falls under that category.

-- Steve